Polar Orbiting Environmental Satellites Research Articles

Prelaunch Reflective Solar Band Radiometric Performance of JPSS-3 and -4 VIIRS

The Joint Polar Satellite System 3 (JPSS-3) and -4 (JPSS-4) Visible Infrared Imaging Radiometer Suite (VIIRS) instruments are the last in the series (S-NPP VIIRS launched in October 2011, JPSS-1 VIIRS launched in November 2017, and JPSS-2 VIIRS launched in November 2022) of highly advanced polar-orbiting environmental satellites. Both instruments underwent a comprehensive sensor-level thermal vacuum (TVAC) testing at the Raytheon Technologies El Segundo facility to characterize the spatial, spectral, and radiometric aspects of the VIIRS sensor performance. This paper focuses on the radiometric performance of the 14 reflective solar bands (RSBs) that cover the wavelength range from 0.41 to 2.3 µm. Key instrument calibration parameters such as instrument gain, signal-to-noise ratio (SNR), dynamic range, and radiometric calibration uncertainty were derived from the TVAC measurements for both the primary and redundant electronics at three instrument temperature plateaus: cold, nominal, and hot. This paper shows that all the JPSS-3 and -4 VIIRS RSB detectors have been well characterized, with key performance metrics comparable to the previous VIIRS instruments on-orbit. The radiometric calibration uncertainty of the RSBs is within the 2% requirement, except in the case of band M1 of JPSS-4. Comparison of the radiometric performance to sensor requirements, as well as a summary of key instrument testing and performance issues, is also presented.

The Relationship Between Electron Precipitation and the Population of Trapped Electrons in LEO: New Evidence Supporting a Natural Limit to the Flux of Energetic Electrons

AbstractEnergetic particle precipitation into the atmosphere has been identified as a key loss process for electrons in the Earth's outer radiation belt region. However, direct measurements of the electron flux precipitating into the atmosphere are challenging from high altitude low inclination spacecraft, such as the Van Allen Probes, due to the small angular size of the loss cone along the orbital path of these high‐altitude spacecraft. Here we use data from the Polar Orbiting Environmental Satellites (POES)/Space Environment Monitor in low‐Earth orbit to assess the relationship between the trapped and precipitating electron flux in integral energy channels >30, >100, and >300 keV. Our results highlight that there is a strong non‐linear relationship between the flux of trapped and precipitating electrons, with the ratio of precipitating to trapped flux only becoming significantly enhanced once the trapped flux reaches a critical level. This transition from low to high levels of precipitation is consistent with the theory proposed by Kennel and Petschek (K‐P) (1966) https://doi.org/10.1029/JZ071i001p00001, whereby intense chorus waves are excited and trigger pitch angle diffusion, resulting in energetic particle precipitation and limiting the trapped flux. Using electron flux data from POES and chorus wave data from the Van Allen Probes, we further test the observations against predictions from the K‐P theory. A particle tracing model is also utilized to illustrate a direct link between the drift paths of injected electrons, the occurrence of chorus waves and the spatial distribution of strong electron precipitation into the atmosphere at different energies.

Electron Precipitation Observed by ELFIN Using Proton Precipitation as a Proxy for Electromagnetic Ion Cyclotron (EMIC) Waves

AbstractElectromagnetic ion cyclotron (EMIC) waves can drive radiation belt depletion and Low‐Earth Orbit satellites can detect the resulting electron and proton precipitation. The ELFIN (Electron Losses and Fields InvestigatioN) CubeSats provide an excellent opportunity to study the properties of EMIC‐driven electron precipitation with much higher energy and pitch‐angle resolution than previously allowed. We collect EMIC‐driven electron precipitation events from ELFIN observations and use POES (Polar Orbiting Environmental Satellites) to search for 10s–100s keV proton precipitation nearby as a proxy of EMIC wave activity. Electron precipitation mainly occurs on localized radial scales (∼0.3 L), over 15–24 MLT and 5–8 L shells, stronger at ∼MeV energies and weaker down to ∼100–200 keV. Additionally, the observed loss cone pitch‐angle distribution agrees with quasilinear predictions at ≳250 keV (more filled loss cone with increasing energy), while additional mechanisms are needed to explain the observed low‐energy precipitation.

Electron Lifetimes Measured at LEO: Comparison With RBSP Estimates and Pitch Angle Resolved Lifetimes

AbstractElectron lifetimes are important for understanding the dominant loss processes of radiation belt electrons to the atmosphere and for accurate radiation belt modeling. We estimate electron lifetimes from the precipitating population measured in Low Earth Orbit (LEO) from the Polar Orbiting Environmental Satellites (POES). We compare our estimates to previous estimates from the Radiation Belt Storm Probes (RBSP) by Claudepierre et al. (2020b, https://doi.org/10.1029/2019GL086053). We also present the first complete pitch angle resolved lifetimes in the radiation belts. Quasi‐linear theory predicts the pitch angle distribution decays uniformly, therefore if steady‐state decay is realized, POES and RBSP should measure similar lifetimes. Lifetime estimates from LEO are shown to be in good agreement with those from Van Allen Probes in the outer belt and pitch angle resolved lifetimes indicate that steady‐state decay is realized. However, a systematic slight overestimation of the POES lifetimes reveal that the POES instruments may suffer from bremsstrahlung contamination. At L = 2–3, no decay intervals were identified in the POES electron fluxes and the near loss cone RBSP electron fluxes. We show that at these L‐shells, where lifetimes are long, there is an apparent decoupling of the perpendicular and parallel flux. Large pitch angle anisotropy and processes that affect low pitch angle electrons are two explanations for this apparent decoupling. Electron lifetime models that use pitch angle independent lifetimes, derived from the equatorially mirroring electron flux, likely underestimate the amount of precipitating flux and may not capture the dynamics of low equatorial pitch angle electrons at L < 3.

Reconstruction of electron radiation belts using data assimilation and machine learning

We present a reconstruction of radiation belt electron fluxes using data assimilation with low-Earth-orbiting Polar Orbiting Environmental Satellites (POES) measurements mapped to near equatorial regions. Such mapping is a challenging task and the appropriate methodology should be selected. To map POES measurements, we explore two machine learning methods: multivariate linear regression (MLR) and neural network (NN). The reconstructed flux is included in data assimilation with the Versatile Electron Radiation Belts (VERB) model and compared with Van Allen Probes and GOES observations. We demonstrate that data assimilation using MLR-based mapping provides a reasonably good agreement with observations. Furthermore, the data assimilation with the flux reconstructed by NN provides better performance in comparison to the data assimilation using flux reconstructed by MLR. However, the improvement by adding data assimilation is limited when compared to the purely NN model which by itself already has a high performance of predicting electron fluxes at high altitudes. In the case an optimized machine learning model is not possible, our results suggest that data assimilation can be beneficial for reconstructing outer belt electrons by correcting errors of a machine learning based LEO-to-MEO mapping and by providing physics-based extrapolation to the parameter space portion not included in the LEO-to-MEO mapping, such as at the GEO orbit in this study.

Modulation Effect of the Annual Cycle on Interdecadal Warming Trends over the Tibetan Plateau during 1998–2020

Abstract The Tibetan Plateau is a sensitive area of global climate change, where few conventional observations exist. Satellite AMSU-A microwave temperature sounding observations of brightness temperature (TB) are located in the absorption band of oxygen, which is well mixed in the atmosphere, and have microwave frequencies varying from 50.3 to 57.6 GHz. Therefore, AMSU-A TB observations at different sounding channels reflect atmospheric temperatures at different altitudes. In this study, AMSU-A TB observations during 1998–2020 from five polar-orbiting environmental meteorological satellites (POESs) are employed to investigate the interdecadal warming/cooling trends over the Tibetan Plateau. A limb correction is first applied to all AMSU-A channels before using TB observations at all fields of view for examining geographic distributions and differences of global warming/cooling trends. It is found that interdecadal trends of upper-tropospheric warming and stratospheric cooling are stronger over the Qinghai Tibetan Plateau than its eastern plain areas. An interdecadal variation of the annual cycle over the Tibetan Plateau is an important factor for the enhanced tropospheric warming trend. We also applied a different approach of significance testing that is based on counting signs of local trends (sign test) and confirmed that the detected significant local trends were not a result of chance. In addition, high-frequency noise in TB observations with periods smaller than annual and semiannual oscillations do not affect the climate trends of TB very much, but significantly reduced the uncertainty of the TB trends over the Tibetan Plateau.

Exploring the Predictability of the High‐Energy Tail of MEE Precipitation Based on Solar Wind Properties

AbstractMedium Energy Electron (MEE) precipitation (≳30 keV) ionizes the mesosphere and initiates chemical reactions, which ultimately can reduce mesospheric and stratospheric ozone. Currently, there are considerable differences in how existing parameterizations represent flux response, timing, and duration of MEE precipitation, especially considering its high‐energy tail (≳300 keV). This study compares the nature of ≳300 to ≳30 keV electron fluxes to better understand differences within MEE precipitation. The MEE fluxes are estimated from measurements by the Medium Energy Proton and Electron Detector (MEPED) onboard the Polar Orbiting Environmental Satellite (POES) from 2004 to 2014. The fluxes are explored in the context of solar wind drivers: corotating high‐speed solar wind streams (HSSs) and coronal mass ejections (CMEs) alongside their associated solar wind properties. Three key aspects of ≳300 keV electron fluxes are investigated: maximum response, peak timing, and duration. The results reveal a structure‐dependent correlation (0.89) between the peak fluxes of ≳30 and ≳300 keV electrons. The epsilon coupling function correlates well (0.84) with the ≳300 keV peak flux, independent of solar wind structure. The ≳300 keV flux peaks 0–3 days after the ≳30 keV flux peaks. The highest probability (∼42%) occurs for a 1‐day delay, while predictive capabilities increase when accounting for solar wind speed. The ≳300 keV flux response has the highest probability of lasting 4 days for both CMEs and HSSs. The results form a base for a stochastic MEE parameterization that goes beyond the average picture, enabling realistic flux variability on both daily and decadal scales.

Ionospheric Modulation by EMIC Wave‐Driven Proton Precipitation: Observations and Simulations

AbstractProtons of tens of keV can be resonantly scattered by electromagnetic ion cyclotron (EMIC) waves excited in the magnetosphere, resulting in proton precipitation down to the upper atmosphere. In this study, we report for the first time the ionospheric height‐dependent ionization in response to EMIC‐associated isolated proton aurora (IPA) using simultaneous space‐borne and ground‐based measurements. On 06 March 2019, the Polar Orbiting Environmental Satellites observed significant proton precipitation in the dusk sector (MLT ∼ 19), while ground‐based magnetometers detected a clear signature of EMIC waves. Meanwhile, the conjugated all sky imager captured an IPA and the nearby Poker Flat incoherent scatter radar (PFISR) showed enhanced electron density in the E region, suggesting a potential consequence of the EMIC wave‐driven proton precipitation. The Global Airglow model simulations confirmed the dominant impact of proton precipitation on the ionosphere and agreed well with PFISR observations. This study confirmed physical links from the magnetosphere to the ionosphere through EMIC‐driven proton precipitation.

Evaluation of the Proton Contamination to MeV Electrons by Solar Proton Events Based on CSES Observations

AbstractThe high energy particle package (HEPP) onboard the China Seismo‐Electromagnetic Satellite (CSES) consists of three subsystems: HEPP‐H, HEPP‐L, and HEPP‐X. HEPP‐H and HEPP‐L detect 0.1–55 MeV electrons and 2–230 MeV protons. HEPP‐X is used to monitor 0.9–35 keV solar X‐rays. The primary objective of this study is to present the measurement techniques and instrument parameters, show the main features of particle observations recorded by these instruments and evaluate the proton contamination to MeV electrons. Based on CSES observation, we report a typical solar X‐ray and solar proton event and compare with observations from Polar Orbiting Environmental Satellites (POES) and Geostationary Operational Environmental Satellites (GOES) satellite. Based on the observations of solar proton events, we put forward one method to evaluate the proton contamination level using comparatively pure proton samples on high L‐shells where the proton flux is near zero at quiet time. The percentage of protons that are mistakenly identified to be electrons by HEPP‐H is estimated to be approximately 0.022%. The proton contaminations only contribute no more than 10% of the total observed electron populations at L = 4 with energy range 8–9 MeV in the outer radiation belt region. Therefore, we conclude that the on‐orbit performance of HEPP instrument has satisfyingly met the design expectations by providing plenty of high‐quality high energy particle observation data and reference for scientific uses in the fields of space weather research and natural hazard monitoring.

Cutoff Latitudes of Solar Proton Events Measured by GPS Satellites

AbstractSolar energetic particles (SEPs), one of the main causes of particle radiation in interplanetary space, can disrupt radio communication, induce spacecraft failures and change the heating and cooling rates in the atmosphere among others. To investigate the impact of SEPs and more specifically solar proton events (SPEs), we established a cutoff latitude database based on energetic particle data from Combined X‐ray Dosimeters (CXDs) on board the Global Positioning System (GPS) spacecraft. Introducing a novel normalization method involving proton fluxes from the Geostationary Operational Environmental Satellites enabled us to include the CXD data from its introduction (2001) onwards. The database contains 5714 cutoff latitudes divided over six energies between 18 and 115 MeV which occur during 58 SPEs from 2001 to 2015. Based on the database, a cutoff latitude parameterization as a function of solar wind dynamic pressure and geomagnetic indices Kp and Dst is created for each energy. Moreover, comparisons to previous studies on energetic particle data from the Polar Orbiting Environmental Satellites have been performed to put the GPS data into perspective. A 1–2° poleward offset is found for the GPS based cutoff latitude models, for which several causes are discussed. Furthermore, the limitation of GPS data to geomagnetic latitudes above 60° should be considered. All in all, the usage of the long time span of GPS data in this study combined with its recent release (2016) opens up a new range of studies involving GPS energetic particle data such as investigating long‐term trends with respect to our solar cycle or magnetospheric trends.

Relativistic Electron Precipitation Near Midnight: Drivers, Distribution, and Properties

AbstractWe analyze the drivers, distribution, and properties of the relativistic electron precipitation (REP) detected near midnight by the Polar Orbiting Environmental Satellites (POES) and Meteorological Operational (MetOp) satellites, critical for understanding radiation belt losses and nightside atmospheric energy input. REP is either driven by wave‐particle interactions (isolated precipitation within the outer radiation belt), or current sheet scattering (CSS; precipitation with energy dispersion), or a combination of the two. We evaluate the L‐MLT distribution for the identified REP events in which only one process evidently drove the precipitation (∼10% of the REP near midnight). We show that the two mechanisms coexist and drive precipitation in a broad L‐shell range (4–7). However, wave‐driven REP was also observed at L < 4, whereas CSS‐driven REP was also detected at L > 7. Moreover, we estimate the magnetotail stretching during each REP event using the magnetic field observations from the Geostationary Operational Environmental Satellite (GOES). Both wave‐particle interactions and CSS drive REP in association with a stretched magnetotail, although CSS‐driven REP potentially shows more pronounced stretching. Wave‐driven REP events are localized in L shell and often occur on spatial scales of <0.3 L. Using either proton precipitation (observed by POES/MetOp during wave‐driven REP) as a proxy for electromagnetic ion cyclotron (EMIC) wave activity or wave observations (from GOES and the Van Allen Probes) at the conjugate event location, we find that ∼73% wave‐driven REP events are associated with EMIC waves.

A New MEPED‐Based Precipitating Electron Data Set

The work presented here introduces a new data set for inclusion of energetic electron precipitation (EEP) in climate model simulations. Measurements made by the medium energy proton and electron detector (MEPED) instruments onboard both the Polar Orbiting Environmental Satellites and the European Space Agency Meteorological Operational satellites are used to create global maps of precipitating electron fluxes. Unlike most previous data sets, the electron fluxes are computed using both the 0° and 90° MEPED detectors. Conversion of observed, broadband electron count rates to differential spectral fluxes uses a linear combination of analytical functions instead of a single function. Two dimensional maps of electron spectral flux are created using Delaunay triangulation to account for the relatively sparse nature of the MEPED sampling. This improves on previous studies that use a 1D interpolation over magnetic local time or L‐shell zonal averaging of the MEPED data. A Whole Atmosphere Community Climate Model (WACCM) simulation of the southern hemisphere 2003 winter using the new precipitating electron data set is shown to agree more closely with observations of odd nitrogen than WACCM simulations using other MEPED‐based electron data sets. Simulated EEP‐induced odd nitrogen increases led to ozone losses of more than 15% in the polar stratosphere near 10 hPa in September of 2003.

Energetic Electron Precipitation Observed by FIREBIRD‐II Potentially Driven by EMIC Waves: Location, Extent, and Energy Range From a Multievent Analysis

AbstractWe evaluate the location, extent, and energy range of electron precipitation driven by ElectroMagnetic Ion Cyclotron (EMIC) waves using coordinated multisatellite observations from near‐equatorial and Low‐Earth‐Orbit (LEO) missions. Electron precipitation was analyzed using the Focused Investigations of Relativistic Electron Burst Intensity, Range and Dynamics (FIREBIRD‐II) CubeSats, in conjunction either with typical EMIC‐driven precipitation signatures observed by Polar Orbiting Environmental Satellites (POES) or with in situ EMIC wave observations from Van Allen Probes. The multievent analysis shows that electron precipitation occurred in a broad region near dusk (16–23 MLT), mostly confined to 3.5–7.5 L‐shells. Each precipitation event occurred on localized radial scales, on average ∼0.3 L. Most importantly, FIREBIRD‐II recorded electron precipitation from ∼200 to 300 keV to the expected ∼MeV energies for most cases, suggesting that EMIC waves can efficiently scatter a wide energy range of electrons.

Comparing Electron Precipitation Fluxes Calculated From Pitch Angle Diffusion Coefficients to LEO Satellite Observations

AbstractParticle precipitation is a loss mechanism from the radiation belts whereby particles trapped by the Earth's magnetic field are scattered into the loss cone due to wave‐particle interactions. Energetic electron precipitation creates ozone destroying chemicals which can affect the temperatures of the polar regions, therefore it is crucial to accurately quantify this impact on the Earth's atmosphere. We use bounce‐averaged pitch angle diffusion coefficients for whistler mode chorus waves, plasmaspheric hiss and atmospheric collisions to calculate magnetic local time (MLT) dependent electron precipitation inside the field of view of the Polar Orbiting Environmental Satellites (POES) T0 detector, between 26–30 March 2013. These diffusion coefficients are used in the BAS Radiation Belt Model (BAS‐RBM) and this paper is a first step toward testing the loss in this model via comparison with real world data. We find the best agreement between the calculated and measured T0 precipitation at L* > 5 on the dawnside for the >30 keV electron channel, consistent with precipitation driven by lower band chorus. Additional diffusion is required to explain the flux at higher energies and on the dusk side. The POES T0 detector underestimates electron precipitation as its field of view does not measure the entire loss cone. We demonstrate the potential for utilizing diffusion coefficients to reconstruct precipitating flux over the entire loss cone. Our results show that the total precipitation can exceed that measured by the POES >30 keV electron channel by a factor that typically varies from 1 to 10 for L* = 6, 6.5, and 7.

Outer Van Allen belt trapped and precipitating electron flux responses to two interplanetary magnetic clouds of opposite polarity

Abstract. Recently, it has been established that interplanetary coronal mass ejections (ICMEs) can dramatically affect both trapped electron fluxes in the outer radiation belt and precipitating electron fluxes lost from the belt into the atmosphere. Precipitating electron fluxes and energies can vary over a range of timescales during these events. These variations depend on the initial energy and location of the electron population and the ICME characteristics and structures. One important factor controlling electron dynamics is the magnetic field orientation within the ejecta that is an integral part of the ICME. In this study, we examine Van Allen Probes (RBSPs) and Polar Orbiting Environmental Satellites (POESs) data to explore trapped and precipitating electron fluxes during two ICMEs. The ejecta in the selected ICMEs have magnetic cloud characteristics that exhibit the opposite sense of the rotation of the north–south magnetic field component (BZ). RBSP data are used to study trapped electron fluxes in situ, while POES data are used for electron fluxes precipitating into the upper atmosphere. The trapped and precipitating electron fluxes are qualitatively analysed to understand their variation in relation to each other and to the magnetic cloud rotation during these events. Inner magnetospheric wave activity was also estimated using RBSP and Geostationary Operational Environmental Satellite (GOES) data. In each event, the largest changes in the location and magnitude of both the trapped and precipitating electron fluxes occurred during the southward portion of the magnetic cloud. Significant changes also occurred during the end of the sheath and at the sheath–ejecta boundary for the cloud with south to north magnetic field rotation, while the ICME with north to south rotation had significant changes at the end boundary of the cloud. The sense of rotation of BZ and its profile also clearly affects the coherence of the trapped and/or precipitating flux changes, timing of variations with respect to the ICME structures, and flux magnitude of different electron populations. The differing electron responses could therefore imply partly different dominant acceleration mechanisms acting on the outer radiation belt electron populations as a result of opposite magnetic cloud rotation.

On the Acceleration Mechanism of Ultrarelativistic Electrons in the Center of the Outer Radiation Belt: A Statistical Study

AbstractUsing energetic particle and wave measurements from the Van Allen Probes, Polar Orbiting Environmental Satellites (POES), and Geostationary Operational Environmental Satellite (GOES), the acceleration mechanism of ultrarelativistic electrons (>3 MeV) in the center of the outer radiation belt is investigated statistically. A superposed epoch analysis is conducted using 19 storms, which caused flux enhancements of 1.8–7.7 MeV electrons. The evolution of electron phase space density radial profile suggests an energy‐dependent acceleration of ultrarelativistic electrons in the outer belt. Especially, for electrons with very high energies (~7 MeV), prevalent positive phase space density radial gradients support inward radial diffusion being responsible for electron acceleration in the center of the outer belt (L*~3–5) during most enhancement events in the Van Allen Probes era. We propose a two‐step acceleration process to explain the acceleration of ~7 MeV electrons in the outer belt: intense and sustained chorus waves locally energize core electron populations to ultrarelativistic energies at high L region beyond the Van Allen Probes' apogee, followed by inward radial diffusion which further energizes these populations to even higher energies. Statistical results of chorus wave activity inferred from POES precipitating electron measurements as well as core electron populations observed by the Van Allen Probes and GOES support this hypothesis.

Properties of Localized Precipitation of Energetic Protons Equatorward of the Isotropic Boundary

AbstractUsing National Oceanic and Atmospheric Administration Polar Orbiting Environmental Satellite (NOAA/POES) observations of energetic protons, we for the first time investigated statistical properties of a specific type of particle precipitation—localized precipitation of energetic protons (LPEP) equatorward of the isotropy boundary. The maximum occurrence rate was found in the day‐afternoon sector at L > 6. The maximum precipitating flux is found at lower L shells (L = 4–5). The dependence of LPEP occurrence and intensity on the geomagnetic activity indices and solar wind parameters is investigated. In particular, while the precipitating proton flux increases with geomagnetic activity everywhere, the occurrence rate in the day‐afternoon sector at L > 6 decreases under the strongest activity. We conclude that revealed LPEP properties are mostly similar to those obtained for electromagnetic ion cyclotron waves on the basis of data from previous spacecraft missions. This similarity supports the suggestion on LPEP as the result of ion cyclotron instability in the magnetosphere.

Atmospheric Effects of >30‐keV Energetic Electron Precipitation in the Southern Hemisphere Winter During 2003

AbstractThe atmospheric effects of precipitating electrons are not fully understood, and uncertainties are large for electrons with energies greater than ~30 keV. These electrons are underrepresented in modeling studies today, primarily because valid measurements of their precipitating spectral energy fluxes are lacking. This paper compares simulations from the Whole Atmosphere Community Climate Model (WACCM) that incorporated two different estimates of precipitating electron fluxes for electrons with energies greater than 30 keV. The estimates are both based on data from the Polar Orbiting Environmental Satellite Medium Energy Proton and Electron Detector (MEPED) instruments but differ in several significant ways. Most importantly, only one of the estimates includes both the 0° and 90° telescopes from the MEPED instrument. Comparisons are presented between the WACCM results and satellite observations poleward of 30°S during the austral winter of 2003, a period of significant energetic electron precipitation. Both of the model simulations forced with precipitating electrons with energies >30 keV match the observed descent of reactive odd nitrogen better than a baseline simulation that included auroral electrons, but no higher energy electrons. However, the simulation that included both telescopes shows substantially better agreement with observations, particularly at midlatitudes. The results indicate that including energies >30 keV and the full range of pitch angles to calculate precipitating electron fluxes is necessary for improving simulations of the atmospheric effects of energetic electron precipitation.

New Homogeneous Composite Of Energetic Electron Fluxes From POES: 2. Intercalibration of SEM‐1 and SEM‐2

AbstractOne of the most popular long‐term data sets of energetic particles used in, for example, long‐term radiation belt studies and in atmospheric/climate studies is perhaps the NOAA/POES (Polar Orbiting Environmental Satellites) data set, which extends nearly continuously from 1979 to present. The present study aims to construct a new homogeneous long‐term composite record of daily latitude distributions of energetic electrons based on the MEPED (Medium Energy Proton and Electron Detector) data. Part 1 of this study corrected the data for temporally varying background noise related to cosmic rays and for the drift in the orientation of satellite orbital planes. The present paper addresses the final and most severe problem for the data homogeneity, caused by the difference of telescope pointing directions in older SEM‐1 and newer SEM‐2 versions of the MEPED instrument. Because the telescope pitch angles and the electron pitch angle distribution change with latitude, the difference in SEM‐1 and SEM‐2 fluxes depends on latitude and varies from time to time. The systematic flux differences between SEM‐1 and SEM‐2 can range between a factor of 1.5 to more than an order of magnitude. Novel statistical methodology based on principal components and canonical correlation mapping is presented here to robustly transform the daily SEM‐1 electron latitude distributions into SEM‐2 level. The data from different POES satellites are then combined into a spatially and temporally homogeneous composite series, which is well suited, for example, for long‐term studies of radiation belts and precipitation related atmospheric ionization and its chemical and dynamical effects in the atmosphere/climate system.

Are EEP Events Important for the Tertiary Ozone Maximum?

AbstractEnergetic particle precipitation (EPP) increases the production of odd hydrogen (HOX) species in the mesosphere, which catalytically destroy ozone (O3) in sunlight. Hence, the EPP‐HOX impact on the tertiary O3 maximum (TOM) depends on a complex geometry of a geographic‐oriented TOM, geomagnetic‐oriented auroral zone, producing short‐lived HOX species, and a destruction process depending on the solar zenith angle (SZA). Particle observations from the Medium Energy Proton and Electron Detectors telescopes aboard the Polar Orbiting Environmental Satellites, and hydroxyl (OH) and O3 mixing ratios from Aura microwave limb sounder (MLS) are used to investigate the potential limitations of using the MLS observations to study EPP‐OH impact on the TOM in the Northern Hemisphere. Our results show limited overlap between the auroral zone and the TOM at twilight conditions. A composite analysis indicates O3 mixing ratio decrease over the auroral zone lagged by ∼1 day compared to the maximum energetic electron precipitation (EEP)‐OH impact. Hence, MLS is predominantly observing a lagged and lower estimate of the response of O3 to EEP‐OH at SZA > 95°. The EEP impact region within the TOM is smaller than the overlap region, strongly modulated by the background atmospheric dynamics. The results, although limited by the satellites viewing conditions, imply that the importance of EEP upon O3 mixing ratio is strongly influenced by the background atmosphere, both in terms of chemistry and dynamics. Multisatellite observations at different solar local times are required to separate the direct from the lagged EEP‐OH impact on O3.